Charles e



(No Model.)

G. E. SCRIBNER.

TEST CIRCUIT FOR MULTIPLE SWITGHBOARDS. 7 No. 477,579. Patented June 21,1892.

switch in which the plug is inserted.

UNITED STATES ATENT iuucn.

CHARLES E. SCRIBNER, OF CHICAGO, ILLINOIS, A SSIGNOR TO THE WESTERNELECTRIC COMPANY, OF SAME PLACE.

TEST-CIRCUIT FOR MULTIPLE SWITCHBOARDS.

SPECIFICATION forming part of Letters Patent No. 477,579, dated June 21,1892.

Application filed May 12, 1885.

To all whom it may concern.-

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States,residing at Ohicago, in the county of Cook and State of Illinois, haveinvented a certain new and useful Improvement in Test-Circuits forMultiple Switchboards, (Case No. 97,) of which the following is a full,clear, concise, and exact description, reference being had to theaccompanyingdrawings, forming a part of this specification.

My invention relates to multiple-switchboard circuits; and it consistsin providing a battery in the ground-circuit of the telephonelines atthe central office and testing apparatus at the different boards,whereby it may be determined at any given board whether a line wanted isin use at an y of the other boards.

In the drawings, which are illustrative of my invention, Figure 1 showsthe circuits of two telephone lines connected with their switches onthree different boards, the battery in the common ground of said lines,and the testing apparatus. Fig. 2 is a detailed View of the plug, theshank of which, except the point, being provided with a sleeve ofinsulating material.

Referring now to Fig. 1, A B C are three multiple switchboards. Thetelephone-line It is connected through a spring-jack switch on eachboard, and thence through the annunciator and the battery to ground. Thetelephone-line b in like manner is connected with a switch on each ofthe boards through its annunciatorand battery to ground. The spring ofeach switch is insulated from the metallic frame.

When a plug is inserted in a switch, the spring only comes intoelectrical contact therewith, since the portion of the plug which comesagainst the metallic tube or frame of the switch is insulated, as shownin Fig. 2. Thus when a plug is inserted the spring is lifted fromcontact with the opposing point or lug provided on the frame, and theline is thus cut off from all succeeding switches and connected to theflexible cord. The portion of the line thus cut off will be open at theThus line a is cut off by switch 0 and connected to Serial No. 165,278.(No model.)

switchman at any given board is able to cut off a line from allsucceeding boards. pro- Vide a batteryfin a local circuit including asignal-instrument at each board and switching apparatus for said circuitand pairs of flexible conducting cords and plugs.

It is by means of the test-batteries and signal-instruments at thedifferent boards, the operators telephone, and the battery gin theground-wire of the telephone-lines that Iain enabled to test todetermine at any given board whether a line wanted is busy. All thespring-jacks of any given line that is free will be found connected withbattery g. On the contrary,lines when busy are cut off from said battery9 by the switch of the line at which the connection is made. Thus line ais cut off from battery 9 at switch 0, as before described. It will beseen, however, that switches 72. and t of said line upon boards B and C,respectively, remain connected with said battery g. By closing thecircuit of a telephone to either of said switches current from battery 9will be sent through the telephone and the presence of the current willbe indicated by the click or sound heard when the circuit is closed.Thus at board 0 the telephone n is shown included in circuit of battery9. Thus the circuit may be traced from ground through battery 9 by linea as far as switch 2', and thence to the tip of the plug, which istouching the test-frame of switch 2', thence through the strand of thecord, and thence, as shown, through the telephone, and thence throughthe other cord to the metallic heel of the plug resting in its socket atboard C, and thence from the plate on which said heel rests to ground.The operator listening at the telephone and hearing the signal when thecircuit is thus closed will know that the line is not connected at anyspring-jack between his board and battery g, and therefore that he canuse the line without crossing in upon any other connection. This test,however, does not indicate whether the line is connected at someprecedingboard. 10o

In order to do this, I provide at the different boardssignal-instruments 7c Z, each in the circuit of battery f.

By connecting the circuit of the signal-instrument and battery at anygiven board with the insulated spring of any spring-jack upon said boardcurrent will be sent to the line connected with said spring-jack and thesignal-instrument will be operated, provided said line is free. If,however, the line is in use at some preceding board, thesignal-instrument will not respond, as the circuit will be open in thespring-jack at which the line is in use, and the operator will thus beapprised of the fact that the line is connected at a preceding board.Thus by means of a telephone m or a, connected to the spring-jack of anygiven line, the operator may determine whether said line is in use atsome succeeding board, and by means of a signal-instrument It or Z,connected with the spring of the spring-jack of anyline, it may bedetermined whether the line is in use at some preceding board.

Having thus described my invention, I claim as new and desire to secureby Letters Patent 1 1. In a multiple-switchboard system, spring jackswitches, one spring-jack switch on each board for each line, eachspring-jack switch consisting of a metallic tube or frame and a springinsulated therefrom, the telephonelines connected through theirrespective spring-jack switches on the different boards to aground-circuit including battery, a pair of cords and terminal plugs ateach of the boards, one of said plugs being normally grounded, and aswitch in connection with each pair of cords for bringing the operatorstelephone into the circuit of any particular pair of cords at eitherofthe boards, whereby a test may be made of any board to determine whetherany given line is open at any succeeding board.

2. The combination, with telephone-lines, each connected with adifferent spring-jack on each of the switchboards and thence through abattery to ground, of operators testing apparatus consisting of atelephone to indicate the presence of battery, together with anelectro-magnetic signal and a test-bat.- tery, whereby a test may bemade toward ground and toward the subscribers station over any line fromany board to determine whether a line is busy.

3. Multiple switchboards and telephonelines connected therewith, asource of electricity for sending electric current upon all the lines ofthe exchange, and an electromagnetic device for indicating such current,in combination with an electromagnetic nal and test-battery to indicatea broken or open circuit existing upon any one of said lines at anotherboard, whereby it may be determined at one board whether any particularline is connected or in use at any other board.

In witness whereof I hereunto subscribe my

